Sedimentary Evidence for Land Use Change in the Narragansett Bay Watershed: Late Woodland period (~500 AD) to the present

In the U.S., the last ~300 years have been a period of progressive and widespread resource exploitation, ecosystem degradation, and habitat destruction. In southern New England, the European Colonists thrived on the spread of slave-based plantation farming, which peaked ~1750 in RI. They produced commodities such as livestock, apples, onions, flax, and dairy. Trees felled to produce the necessary pasture- and farm-land were quickly used as lumber for boards, planks, timber, and barrels. In 1793, Slater Mill, located on the Blackstone River at the head of Narragansett Bay, was the first mill in the U.S to spin yarn using water power, making it the birthplace of the U.S Industrial Revolution. The ensuing urbanization drove the human population of the watershed up from ~50,000 in 1790 to more than 2 million by the year 2000. More recently, the Bay has experienced episodic hypoxic events [1]. These events correlate well with spatial and temporal patterns of nutrients and productivity [2] suggesting that human-induced increases in nutrient nitrogen and phosphorus are responsible for eutrophication-induced oxygen depletion [3]. However, these post-Colonial land use changes have yet to be characterized within the longer context of Native American land use practices, mainly due to the lack of historical records for the period. Additionally, the impact of this ecosystem disturbance on the Bay has not been fully described. Here we present results based on sedimentary profiles of biomarkers diagnostic for soil delivery to marine systems, branched glycerol dialykl glycerol tetraethers, and pollen for disturbance taxa, that suggest land use change began in the Bay's watershed 300 years before European contact. This contradicts long standing ideas regarding the land use practices of local tribes but agrees with new archaeological findings suggesting large semi-permanent settlements and widespread horticulture of maize may have been the norm at this time. We also show results of pollen, nitrogen isotopes, and foraminiferal abundance (proxies for land disturbance, nutrient sources, and ecosystem productivity, respectively) implying the large domestic animal population housed on the plantations were a new source of nitrogen to the Bay. This nutrient input may have led to an increase in the Bay's primary productivity, which may have decreased or stabilized as plantations became less important. Lastly, these same proxies show that the industrialization and urbanization of the Bay's watershed added additional nutrients, further stimulating the Bay's productivity. 1. Codiga, D.L., et al., Narragansett Bay Hypoxic Event Characteristics Based on Fixed-Site Monitoring Network Time Series: Intermittency, Geographic Distribution, Spatial Synchronicity, and Interannual Variablity. Estuaries and Coasts, 2009. 32: p. 621-641. 2. Oviatt, C.A., Impacts of Nutrients on Narragansett Bay Productivity: A Gradient Approach, in Science for Ecosystem-based Management, Narragansett Bay in the 21st Century, A. Desbonnet, Editor 2008, Springer: New York. p. 523-543. 3. Nixon, S.W., et al., Nitrogen and Phosphorus Inputs to Narragansett Bay: Past, Present, and Future, in Science for Ecosystem-based Management: Narragansett Bay in the 21st Century, A. Desbonnet and B.A. Costa-Pierce, Editors. 2008, Springer: New York, NY. p. 101-175.